Displacement constraints on slave nodes in bonded contact

PaulFlynn

I understand you can't have additional constraints on slave nodes in a bonded contact, but is there a way to delete the constraints on the slave nodes where a symmetry surface and the bonded contact intersect?

In old days, before GUI, you just go into the deck and delete the displacement constraint lines for the offending nodes.  (I'm showing my age)  Can you do this in MECWAY or CCX.  

Paul

PaulFlynn

Ok,  I guess I'll answer my own question.  Set up the model with the redundant BC's on the symmetry plane and the bonded contact.  Run CCX.  It will fail, but it will write out the input file.  

Open the input file and copy the *BOUNDARY lines.  Paste the *BOUNDARY lines in the CCX step window.  This is feasible now that the 32k character limit is removed from the new version.   Delete the offending SPC's in the step window.  Suppress the symmetry BC's in MECWAY. Run CCX.

This time it will run correctly using the edited BC's in the step window.  

This is kind of cluegy, but it works.  Hopefully a cleaner process will be available in the future.   Why not just check for redundant slave BC's when you write the CCX file and don't write them to begin with.

Paul

Victor

That's a good idea to have it automatically remove the conflicting nodes. It won't be quite correct unless the constraint is on all DOFs so it would need to come with a warning, but still a worthwhile compromise.

You can use the GUI to remove the element faces that are shared by both bonded contact and other constraints (Select the faces, right click the constraint and choose Remove faces). But then you get a slightly bigger unconstrained region than from just the nodes along the edge.

The easiest way with mirror symmetry is usually to use elastic support (sliding constraint on distributed normal springs) with a large stiffness so it behaves like frictionless support. Since this is a penalty constraint, it won't conflict with any contacts or constraint equations. You've got a more complicated mirror symmetry though and I'm not sure if/why elastic support wouldn't suit.

Victor

I just found that CCX's *TIE seems to be quite happy with constraints sharing its nodes. Sometimes it appears to release the contact where constraints are on slave nodes but not always. You can easily get bonded contact in to use *TIE by checking that box in the bonded contact's window.